1. Field of the Invention
This invention relates to a method for attaching cells to a surface, and more specifically relates to a method for depositing a layer of endothelial cells on a polymeric surface and to surfaces prepared thereby.
2. Background of the Invention
Extensive investigations have been undertaken over many years to find materials that will be biologically and chemically stable toward body fluids. This area of research has become increasingly important with the development of various objects and articles which can be in contact with blood, such as artificial organs, vascular grafts, probes, cannulas, catheters and the like.
Synthetic plastics have come to the fore as preferred materials for such articles. However, such materials have the major drawback of being thrombogenic. Even such plastics as polytetrafluoroethylene and the silicone rubbers which are more compatible with blood than most plastics, still show thrombogenic characteristics.
Thrombogenicity has conventionally been counteracted by the use of anticoagulants such as heparin. Exemplary of heparinization procedures are the disclosures in U.S. Pat. No. 4,613,517 to Williams et al. and U.S. Pat. No. 4,521,564 to Solomon et al.
Over the past three decades, artificial grafts have been used to restore blood flow to areas of ischemia, to provide blood flow for hemodialysis patients and for repair of arterial aneurysms. While these procedures are generally initially successful, long term prognosis for patients receiving such grafts is not encouraging, principally because small diameter grafts (4 mm or less) become occluded over time due to fibrin deposition and cellular adhesion due to the thrombogenic nature of the graft material.
The ideal blood-surface interface has long been considered to be the naturally occurring human endothelium, and much current research is focused on endothelialization procedures. Madri et al. in the Journal of Cell Biology 97, 153 (1983) reported that when cells are grown on interstitial collagens, they undergo proliferation and form a continuous cell layer. Williams et al., Journal of Surgical Research 38, 618 (1985) described pretreatment of prosthetic graft material with fibronectin, collagen or blood plasma, and reported that essentially no adherence occurred on untreated graft material, but that dramatic increases in adherence occurred on protein-coated polyester grafts. A similar study by Jarrell et al. (Annals of Surgery, 203, 671 (1986)) showed a high percentage of firm adherence of endothelial cells to polyester coated with platelet-rich-plasma in 10 min., to amnion/collagen coated polyester in 30 min. and to plain polyester in two hours, but that only the amnion/collagen coated surface exhibited complete graft coverage.
In recent years, attention has focused upon the poor results generally obtained with small diameter vascular grafts. van Wachem et al., in Biomaterials 6, 403 (1985) reported clinical success with polymeric grafts of greater than 4 mm, but that grafts of less than 4 mm gave generally disappointing clinical results due to immediate occlusion. Likewise, Baker et al., in American Journal of Surgery 150, 197 (1985) stated that long term patency of large diameter vascular grafts is relatively acceptable, but small diameter (less than 4 mm) grafts exhibit poor long-term patency rates.
Seeding of 4 mm inside diameter polyester vascular grafts with endothelial cells and patency after implantation in dogs is discussed by Belden et al. in Trans. Am. Soc. Artif. Intern. Organs. 28, 173 (1982).
Modification of polymeric surfaces by treatment with a variety of plasmas to achieve certain results is well known. For example, surface wettability, static properties and receptivity of a surface to deposition of a layer of an adherent polymeric material have been described. The doctoral thesis of Lee M. Smith, "Cell Adhesion As Influenced By Substrate Surface Properties", Department of Material Science and Engineering, the University of Utah, 1978, p. 67, suggests that cell adherence is a function of the carbon/oxygen ratio of the surface. van Wachem et al., (supra) discloses that endothelial cells can be cultured on glass or glow-discharge treated polystyrene.
U.S. Pat. No. 4,452,679 to Dunn et al. discloses a method to modify a polymeric surface to introduce specific chemical groups by treatment of the surface with a plasma in which at least one of the neutral, positive or negative species of the plasma is excluded from contacting the surface.
Applicants are also aware of a disclosure that endothelial cells adhere partially, but not confluently, to an untreated Dacron.TM. polyester surface, that this surface will become confluently covered in 24 hours, and that near confluent coverage occurs with a Dacron.TM. surface pretreated with a protein, such as platelet rich plasma. In the present disclosure, the term confluent is used to describe a surface which is substantially covered with cells which are contiguous in all directions.
In spite of the extensive investigations on antithrombogenic prosthetic devices, the problem of thrombogenicity has not been satisfactorily solved, in particular with respect to small diameter grafts. It is toward the solution of this problem that the current invention is directed.